This proposal requests four years of support (411/00-3131104) to study the epidemiology, correlates and risk factors for nicotine dependence in a national longitudinal sample of US youths 18 to 24 years old, the National Longitudinal Study of Adolescent Health (Add Health) (Resnick et al., 1997; Udry, 1998). Funds are requested to cover the inclusion of additional interview data on nicotine dependence and two hypothesized risk factors not previously ascertained in the next wave of data collection to be implemented in the year 2000 (Wave III Survey 2000). The proposed research has three specific aims: (1) To describe the epidemiology and natural history of nicotine dependence and other aspects of smoking behavior, in particular lifetime smoking, daily smoking and quantity smoked, among US youths. (2) To identify psychological and social factors that correlate and predict smoking onset, daily smoking, quantity smoked and nicotine dependence (risk factors) and factors that reduce the risk of onset, daily smoking, quantity smoked and nicotine dependence (protective factors). (3) To identify gender and ethnic commonalties and differences with respect to Aims #1 and #2. To achieve these aims, additional data will be obtained in the third wave of Add Health data collection on over 20,000 youth aged 18-24, first interviewed at ages 12-18. The sample constitutes a national representative sample of former 7th-12th graders, and includes a genetically informative sample of twin, full sibling, half sibling and unrelated pairs. With the addition of the new questions, unique data on the epidemiology of nicotine dependence will be available for a nationally representative sample of US youths, with a rich source of longitudinal information. These data will be available to other investigators since Add Health data are released as a public use data set. The proposed study will generate a unique understanding of the epidemiology, natural history, correlates and etiology of smoking and nicotine dependence among young people